Axial Brushless DC Motor

ABSTRACT

An axial brushless DC motor comprising a stator, a rotor including a magnet, a sleeve bushing extending through the stator and including a pair of opposed distal collars, a motor shaft extends through the sleeve bushing, and a pair of opposed bearings are seated in the respective pair of collars and mount the shaft and a rotor for rotation relative to the sleeve bushing and the stator. The bearings are adapted for thrust, radial support/self-alignment, and angular adjustment of the motor shaft. In one embodiment, a stator overmold member includes a central tube that defines the sleeve bushing and includes a stator shorting ring. In one embodiment, a metal pole piece is seated in a cup-shaped magnet with a rim and the magnetic flux travels through the rim of the magnet and through a magnetic flux sensor.

CROSS-REFERENCE TO RELATED AND CO-PENDING APPLICATIONS

This patent application is a continuation application that claimspriority and benefit of the filing date of U.S. patent application Ser.No. 15/017,237 filed on Feb. 5, 2016, the disclosure and contents ofwhich is expressly incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates generally to a motor and, in particular,to an axial brushless DC motor.

BACKGROUND OF THE INVENTION

There is a continued need for smaller and more cost effective axialbrushless DC motors that provide the same output performance as largerand less cost effective axial brushless DC motors. The present inventionsatisfies this need.

SUMMARY OF THE INVENTION

The present invention is generally directed to an axial brushless DCmotor comprising a stator, a rotor including a magnet, an elongatesleeve bushing extending through the stator, the sleeve bushing definingan interior through-aperture and including first and second opposeddistal bearing collars, an elongate shaft extending through the interiorthrough-aperture of the sleeve bushing, a first bearing in the firstbearing collar in the sleeve bushing and surrounding a first end of theshaft for allowing the rotation of the shaft relative to the sleevebushing and the stator, and a second bearing in the second bearingcollar in the sleeve bushing and surrounding a second opposed end of theshaft for allowing the rotation of the shaft and the rotor relative tothe stator.

In one embodiment, the second bearing is a thrust ball bearing includingballs sandwiched between opposed upper and lower bearing races, theupper and lower bearing races including respective collars havingrespective ball bearing abutment surfaces that allow for the combinationof thrust, radial support/self-alignment, and angular adjustment of thebearing races relative to each other and the shaft supported by thethrust ball bearing.

In one embodiment, the second bearing is a thrust ball bearing includingballs sandwiched between opposed upper and lower bearing races, theupper and lower bearing races including respective collars havingrespective ball bearing abutment surfaces, one of the upper and lowerbearing abutment surfaces following the contour of the balls and theother of the upper and lower ball bearing abutment surfaces being anangled and flat surface.

In one embodiment, the ball bearing abutment surface on the upperbearing race follows the contour of the balls and the ball bearingabutment surface on the lower bearing race is angled and flat to allowfor the combination of thrust, self-centering, radial support, andalignment of the bearing races relative to each other and the shaft thatis supported by the thrust bearing.

In one embodiment, the ball bearing abutment surface on the upperbearing race is angled and flat and the ball bearing abutment surface onthe lower bearing surface follows the contour of the balls to allow thecombination of thrust, radial support, and self-alignment of the bearingraces relative to each other and the shaft that is supported by thethrust bearing.

In one embodiment, the first and second bearings are located in thefirst and second bearing collars in a back-to-back relationship.

In one embodiment, a stator overmold member surrounds the coils anddefining the sleeve bushing and a housing for the rotor.

In one embodiment, a stator shorting ring includes respective terminalscoupled to the respective coils, the stator shorting ring extending inthe stator overmold member.

In one embodiment, the stator includes a plurality of coils arranged inrespective pairs of coils connected in parallel.

In one embodiment, the stator includes a plurality of coils arranged inrespective pairs of coils connected in series.

In one embodiment, a cup-shaped magnet defines a receptacle for adisc-shaped metal pole piece.

In one embodiment, the cup-shaped magnet includes a rim and is adaptedto generate a magnetic flux, the magnetic flux being adapted to travelthrough the rim of the magnet and through a magnetic flux sensor.

In one embodiment, the metal pole piece defines a notch in a peripheralregion thereof located adjacent the rim of the magnet for enhancing thedensity of the magnetic flux in the region of the rim of the magnet andthe magnetic flux sensor.

The present invention is also directed to an axial brushless DC motorcomprising a stator including a plurality of coils, a stator overmoldmember surrounding the coils and defining a sleeve bushing includingfirst and second bearing collars and a housing for the rotor, a rotorincluding a magnet and located in the rotor housing defined in thestator overmold member, a motor shaft extending through the sleevebushing of the stator overmold assembly and coupled for rotation to andwith the rotor, and first and second bearings seated in the respectivefirst and second bearing collars in the sleeve bushing of the statorovermold assembly and mounting the motor shaft in the motor for rotationwith the rotor relative to the stator.

In one embodiment, a stator shorting ring includes terminals coupled tothe coils, the stator over mold member surrounding the stator shortingring.

The present invention is further directed to an axial brushless DC motorcomprising a stator, a rotatable motor shaft extending through thestator, and a rotor overlying and spaced from the stator and coupled forrotation with the motor shaft, the rotor including a magnet thatgenerates a magnetic flux adapted for sensing by a magnetic flux sensor,the magnet including a rim and the magnetic flux sensor overlying andspaced from the rim of the magnet, the magnetic flux being adapted totravel through the rim of the magnet and the magnetic flux sensor.

In one embodiment, the magnet is in the shape of a cup including the rimand further comprising a metal pole piece seated in the cup-shapedmagnet and includes a peripheral notch formed therein in a region of themagnet pole piece adjacent the rim of the magnet for enhancing thedensity of the magnetic flux in the region of the rim and the magneticflux sensor.

There are other advantages and features of this invention which will bemore readily apparent from the following description of the embodimentof the invention, the drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings that form part of the specification, and inwhich like numerals are employed to designate like parts throughout thesame:

FIG. 1 is a perspective view of an axial brushless DC motor inaccordance with the present invention;

FIG. 2 is a vertical cross-sectional view of the axial brushless DCmotor in accordance with the present invention;

FIG. 3 is an exploded view of the axial brushless DC motor in accordancewith the present invention;

FIG. 4 is an enlarged vertical cross-sectional view of one embodiment ofthe thrust/radial bearing of the axial brushless DC motor in accordancewith the present invention;

FIG. 5 is an enlarged vertical cross-sectional view of anotherembodiment of the thrust/radial bearing of the axial brushless DC motorin accordance with the present invention;

FIG. 6 is an enlarged vertical cross-sectional view of a furtherembodiment of the thrust/radial bearing of the axial brushless DC motorin accordance with the present invention;

FIG. 7 is a simplified top plan view of the stator of the axialbrushless DC motor in accordance with the present invention;

FIG. 8 is a schematic diagram of an electrical circuit for the parallelconnection and coupling of the coils of the stator of the axialbrushless DC motor in accordance with the present invention;

FIG. 9 is a schematic diagram of an electrical circuit of the seriesconnection and coupling of the coils of the stator of the axialbrushless DC motor in accordance with the present invention;

FIG. 10 is a perspective view of an embodiment of an axial brushless DCmotor in accordance with the present invention with a stator over moldmember;

FIG. 11 is a vertical cross-sectional view of the axial brushless DCmotor shown in FIG. 10;

FIG. 12 is an exploded perspective view of the axial brushless DC motorshown in FIG. 10;

FIG. 13 is a part perspective, part vertical cross-sectional view of theaxial brushless DC motor shown in FIG. 10; and

FIG. 14 is a vertical cross-sectional view of the axial brushless DCmotor in accordance with the present invention with a cupped rotormagnet.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIGS. 1, 2, and 3 depict an axial brushless DC motor 10 in accordancewith the present invention which comprises a stator or stator assembly12, a rotor or rotor assembly 14, a sleeve bushing 16, a ball bearing18, a thrust bearing 20, and an elongate motor shaft 21. In theembodiment shown, the axial brushless DC motor 10 is a three phase,eight pole, six slot axial brushless DC motor.

The stator assembly 12 includes a flat base 22 in the form and shape ofa disc defining a central through-hole or aperture 23, an interiorcircumferential shoulder 24 defined by the interior wall of the base 22defining the central through-hole 23 thereof, and a plurality ofperipheral motor mounting brackets 25 each defining a plurality of motormounting through-holes 27. In the embodiment shown, the base 22 is madefrom a powder metal. A plurality of stator armature posts 25, namely sixin the embodiment of FIGS. 1, 2, and 3, protrude unitarily normallyupwardly and outwardly from the interior face of the base 22. In theembodiment shown, the armature posts 25 are generally triangular inshape and extend full circle around the central through-hole or aperture23 in a spaced apart relationship relative to each other and the centralthrough-hole or aperture 23. Also, in the embodiment shown, therespective side faces 25 a and 25 b of each of the armature posts 25converge inwardly towards each other and in the direction of the centralthrough-hole or aperture 23.

The stator assembly 12 also includes a plurality of elongatethermoplastic bobbins 26 each defining a central elongate core or spool27 defining a central elongate through-hole 27 a. The central elongatecore or spool 27 is of a triangular shape complementary with thetriangular shape of the respective armature posts 25.

Electrical coil packs 28 extend around the core or spool 27 of thebobbins 26 respectively. The bobbins 26 are positioned on the base 22relative to each other such that a slot or gap 30 is defined betweeneach of the bobbins 26 and coils 28. The embodiment shown defines sixslots or gaps 30.

The rotor assembly 14 includes a flat base 32 in the form and shape of adisc defining a central through-hole or aperture 34. The base 32 is madefrom powder metal. A flat magnet 36 is seated against the exteriorsurface of the bottom face 38 of the rotor base 32. In the embodimentshown, the magnet 36 is in the form and shape of a disc and defines acentral through-hole or aperture 39 having a diameter greater than andspaced from the central through-hole or aperture 34 defined in the rotorbase 32. In the embodiment shown, the magnet 36 is made of compressionbonded Neo Ferrite magnetic material and is comprised of eightalternating N-S poles.

The rotor assembly 14 and the stator assembly 12 are positioned relativeto each other in an overlapping relationship with the exterior top faceof the magnet 36 of the rotor assembly 14 positioned opposite, spacedfrom, and parallel to, the exterior top face of the armature posts 25,bobbins 26, and the coils 28 of the stator assembly 12. In thisrelationship, the two pairs of coils 28 (or four coils or two phases)are energized in response to the rotation of the rotor assembly 14 andthe magnet 36 at any commutation stage.

The Estimated Peak Torque Constant per phase for the motor 10 is:

K _(T)(Nm/At) is about B _(air)*(OD ² −ID ²)/4

where:

K_(T) (Nm/At)—Peak Torque Constant

B_(air) (T)—Magnet Flux Density in the Air Gap

OD (m)—Stator and Magnet OD

ID (m)—Magnet ID

The sleeve bushing 16, the bearings 18 and 20, and the motor shaft 21are assembled in a relationship that allows for rotation of the rotorassembly 14 relative to the stator assembly 12 in response to therotation of the motor shaft 21.

The elongated sleeve bushing 16 defines an interior elongated hollowcylindrical bore 40. Radial bearing receiving collars 42 and 44 areformed at opposite ends of the sleeve bushing 16 and are adapted toreceive and seat the ball bearing 18 and the thrust bearing 20respectively. The radial collars 42 and 44 have diameters greater thanthe diameter of the sleeve bushing 16. The upper collar 44 includes aradial portion 44 a that extends radially outwardly and normally fromthe sleeve bushing 16 and an axial portion 44 b that extends outwardlyand upwardly from the distal end of the radial portion 44 a.

The sleeve bushing 16 extends through the center of the motor 10 in arelationship wherein the sleeve bushing 16 is surrounded by the statorarmature posts 25, the bobbins 26, and the coils 28; the collar 42 islocated in the central through-hole 23 defined in the base 22 of thestator assembly 12 and seated against the interior shoulder 24 of thestator base 22; and the collar 44 is located in the through-hole 38defined in the magnet 36. More specifically, the collar 44 is positionedin a relationship with the radial portion 44 a located between thebobbins 26/coils 28 and the magnet 36 and the axial portion 44 bextending into the interior of the through-hole 38. Thus, the sleevebushing 16 extends through the center of the motor 10 and through thestator 12 in a relationship co-linear with the longitudinal axis L ofthe motor 10.

The motor shaft 21, which is elongate and generally cylindrical inshape, extends through the center of the motor 10 and more specificallyextends through the interior bore 40 of the sleeve bushing 16. A firstend of the motor shaft 21 extends through the through-hole 23 defined inthe center of the base 22 of the stator assembly 12 and an oppositesecond end that extends through the through-hole 34 defined in thecenter of the magnet 32 of the rotor assembly 14.

The radial bearing 18 is in the form and shape of a ring and defines acentral through-aperture 19. The radial bearing 18 is nested in thecollar 42 of the sleeve bushing 16 and is located and mounted in themotor 10 in a relationship wherein the radial bearing 18 surrounds thelower end of the motor shaft 21 and the collar 42 of the sleeve bushing16 surrounds the radial bearing 18 thereby mounting the lower end of themotor shaft 21, and thus the motor shaft 21, in the motor 10 forrotation relative to the sleeve bushing 16 and the stator assembly 12.

The bearing 20 is a combination thrust and radial bearing that is alsoin the form and shape of ring defining a central through-aperture 17 andis nested and seated in the interior of the upper collar 44 of thesleeve bushing 16 and in a relationship surrounding the upper end of themotor shaft 21 thereby mounting the upper end of the motor shaft 21, andthus the motor shaft 21 and the rotor 14, for rotation relative to thesleeve bushing 16 and the stator 12.

The bearing 20 is shown in more detail in FIG. 4 and includes acombination of thrust, radial support/self-alignment, and angularadjustment features.

The bearing 20 a shown in FIG. 5 is a bearing that includes acombination of thrust, self-centering, radial support, and alignmentfeatures.

The bearing 20 b shown in FIG. 6 is a bearing that includes acombination of thrust, radial support, and self-alignment features.

The structure of the thrust bearings 20, 20 a, and 20 b allows for thecombination thrust, radial support, radial alignment, and angularadjustment features to be incorporated into a single bearing.

The thrust bearing 20 must include at least the thrust feature and oneof the other features of the thrust bearings shown in FIGS. 4, 5, and 6to assure the proper rotation of the rotor assembly 14 and the shaft 21in response to the centrifugal forces and acceleration when the rotorassembly 14 and the shaft 21 are rotated at a relatively high speed andthus assuring the proper function of the motor 10.

Each of the thrust bearings 20, 20 a, and 20 b prevents movement of therotor assembly 14 and the motor shaft 21 in the X-Y plane and thusmaking the rotor assembly 14 and the motor shaft 21 suitable and adaptedfor high speed and continuous rotation.

The bearing 20 shown in FIG. 4 is comprised of a plurality of metalballs 60 sandwiched between a pair of stacked and generally ring shapedupper and lower bearing races 62 and 64 each defining respective centralthrough-apertures 17 and including respective peripheral andcircumferentially extending collars 63 and 65 having respective arcuateexterior side surfaces defining respective ball bearing receivingrecesses or nests 66 and 68.

In the embodiment of FIG. 4, the collar 63 of the race 62 extends intothe interior 17 of the collar 65 of the race 64 and the arcuate surfacesdefining the respective nests 66 and 68 are positioned in an opposedrelationship and are complementary to and follow the contour of opposedregions of the exterior surface of the ball bearings 60. In theembodiment of FIG. 4, the respective surfaces defining the respectivenests 66 and 68 are formed and curved to allow approximately one half ofthe opposed regions of the exterior surface of the respective balls 60to be nested therein in a relationship with the upper exterior surfaceof the balls 60 nested in the nesting surface 66 of the collar 63 of therace 62 and the lower exterior surface of the balls 60 nested in thenesting surface 68 of the collar 65 of the race 64.

The combination of the use of nests 66 and 68 on the respective bearingraces 62 and 64 with a shape that follows the contour of the balls 60allows the bearing 20 and the bearing races 62 and 64 to serve acombination of thrust, radial support/self-alignment, and angularadjustment functions (as shown in phantom in FIG. 4 which shows thebearing race 62 of the bearing 20 and the shaft 21 positioned at anangle relative to the bearing race 64 and the bearing central verticalaxis) relative to each other and the motor shaft 21 and rotor 14 that issupported by the bearing 20.

The bearing 20 a shown in FIG. 5 is comprised of metal balls 60 asandwiched between a pair of stacked and generally ring shaped upper andlower bearing races 62 a and 64 a each defining respective centralthrough-apertures 17 a and including respective peripheral andcircumferentially extending collars 63 a and 65 a having respectiveexterior side surfaces defining respective opposed ball bearing abutmentsurfaces 66 a and 68 a.

In the embodiment of FIG. 5, the collar 63 a of the race 62 a extendsinto the interior through-aperture 17 a of the collar 65 a of the race64 a; the surface 66 a on the bearing race 62 a is in the form and shapeof a nest that is complementary to and follows the contour of the lowerexterior surface of the balls 60 a and, more specifically, in a form andshape that allows approximately one half of the lower exterior surfaceof the respective balls 60 a to be nested therein; and the surface 68 aon the bearing race 64 a is angled and flat.

Thus, in the embodiment of FIG. 5, the respective balls 60 a are nestedbetween the respective races 62 a and 64 a in a relationship with theupper exterior surface of the respective balls 60 a nested in theexterior surface 66 a of the collar 63 a of the race 62 a and the lowerexterior surface of the respective balls 60 a abutted against the angledand flat abutment exterior surface 68 a of the collar 65 a of the race64 a.

The combination of the use of ball bearing abutment surfaces 66 a and 68a with the shape and configuration as shown in FIG. 5 allows the bearing20 a and the bearing races 62 a and 64 a to serve a combination ofthrust, self-centering, radial support, and alignment functions relativeto each other and the motor shaft 21 and the rotor 14 that is supportedby the bearing 20 a.

The bearing 20 b shown in FIG. 6 is comprised of metal balls sandwichedbetween a pair of stacked and generally ring shaped bearing races 62 band 64 b each defining an interior through-aperture 17 b and includingrespective peripheral and circumferentially extending collars 63 b and65 b having respective exterior side surfaces defining respective ballbearing abutment surfaces 66 b and 68 b. In the embodiment of FIG. 6,the collar 63 b of the race 62 b extends and is located in the interiorof the collar 65 b of the race 64 b; the surface 66 b on the bearingrace 62 b is angled and flat; and the surface 68 b on the bearing race64 b is in the form and shape of a nest that follows the contour of theexterior surface of the balls 60 b and allows approximately one quarterof the exterior surface of the balls 60 b to be nested therein.

Thus, in the embodiment of FIG. 6, the respective balls 60 b are nestedbetween the respective races 62 b and 64 b in a relationship with theupper exterior surface of the respective balls 60 b abutted against theexterior surface 66 b of the collar 63 b of the race 62 b and the lowerexterior surface of the respective balls 60 b nested in the surface 68 bof the collar 65 b of the race 64 b.

The bearing 20 b further comprises a ring spring 65 extending andlocated between a peripheral and circumferentially extending shoulder 69defined and formed on the exterior surface of the collar 63 b of therace 62 b and a peripheral and circumferentially extending shoulder 71defined and formed on the exterior surface of the collar 65 b of therace 64 b.

The combination of the use of ball bearing abutment surfaces 66 b and 68b with the shape and configuration as shown in FIG. 6 allows the bearing20 b and the bearing races 62 b and 64 b to serve a combination ofthrust, radial support, and self-alignment functions relative to eachother and the motor shaft 21 that is supported by the bearing 20 b.

The respective bearings 20, 20 a, and 20 b are mounted in the collar 44of the sleeve bushing 16 in a relationship wherein, during operation ofthe motor 10, the respective bearing races 62, 62 a, and 62 b rotaterelative to the respective bearing races 64, 64 a, and 64 b to allow therotation of the motor shaft 21 and the rotor assembly 14 relative to thestator assembly 12.

FIG. 8 depicts the parallel circuit schematic and arrangement of theaxial motor 10 shown in FIGS. 1, 2, and 3 with the stator coilarrangement shown in FIG. 7.

Specifically, FIG. 8 depicts the coils 28 arranged on the stator 12 in arelationship wherein respective pairs of the coils 28 define therespective phases U, V, and W of the stator 12 with the pair of coils 28defining the U phase positioned in an opposing and co-linearrelationship, the pair of coils 28 defining the V phase positioned in anopposing and co-linear relationship, the pair of coils 28 defining the Wphase positioned in an opposing and co-linear relationship, and thecoils 28 extending around the stator 12 in an alternating phaserelationship with the V phase coils 28 located between the U and W phasecoils 28.

Specifically, FIG. 8 shows the two coils 28 defining the U phaseconnected in parallel, the two coils 28 defining the V phase connectedin parallel, and the two coils 28 defining the W phase connected inparallel.

FIG. 9 depicts an alternate series circuit schematic and arrangement forthe axial motor 10 in which the coils have been arranged in the phasesU, V, and W as shown in FIG. 7 with the two coils 28 defining the Uphase connected in series, the two coils 28 defining the V phaseconnected in series, and the two coils 28 defining the W phase connectedin series.

The series circuit arrangement of FIG. 9 is advantageous in highervoltage, for example 24 V, applications while the parallel circuitarrangement of FIG. 8 is advantageous in lower voltage, for example 12V, applications.

FIGS. 10, 11, 12, and 13 depict another embodiment of an axial brushlessDC motor 110 in accordance with the present invention which comprises astator assembly 112, a rotor assembly 114, a pair of ring shapedthrust/radial bearings 118 and 120, and an elongate motor shaft 121. Inthe embodiment shown, the axial brushless DC motor 110 is a three phase,six pole, axial brushless DC motor.

The stator assembly 112 includes a flat base or armature 122 in the formand shape of a disc defining a central through-hole or aperture 124, anda plurality of motor mounting brackets 121 each defining at least onemotor mounting through-hole 123. In the embodiment shown, the base 122may be made from a powder metal. A plurality of metal stator armatureposts 125, namely six in the embodiment shown, protrude unitarilyupwardly and outwardly from the interior face of the base 122. In theembodiment shown, the posts 125 are generally triangular in shape andextend full circle around the central through-hole or aperture 124 in aspaced apart relationship relative to each other and the centralthrough-hole or aperture 124. Also, in the embodiment shown, therespective side faces 125 a and 125 b of each of the posts 125 (FIG. 12)converge inwardly towards each other and in the direction of the centralthrough-hole or aperture 124.

The stator assembly 112 also includes a plurality of elongatethermoplastic bobbins 126 each defining a central elongate core or spool127 defining a central elongate through-hole 127 a. The central elongatecore or spool 127 is of a triangular shape complementary with thetriangular shape of the respective armature posts 125.

An electrical metal coil pack 128 extends and is wound around theexterior face of the core or spool 127 of each of the bobbins 126. Eachof the coil packs 128 includes a pair of bent distal terminal ends 128 aand 128 b positioned in a side-by-side and spaced relationship relativeto each other and adapted to extend through the interior of respectivehollow and side by side and spaced bobbin connectors 126 a and 126 bformed at the top of each of the bobbins 126.

The stator assembly 112 further includes a plurality of, namely six inthe embodiment shown, electrical metal terminals 129 adapted forelectrical coupling and connection to the distal end 128 a of each ofthe six coils 126 respectively.

The stator assembly 112 still further includes a generally ring shapedelectrical metal shorting bar or ring 131 that includes a plurality of,namely six in the embodiment shown, spaced apart and circumferentiallyextending electrical metal terminals 131 b unitary with the shortingring 31 and adapted for electrical coupling and connection to the distalterminal end 128 b of each of the six coil packs 126 respectively.

The stator assembly 112 still further comprises a thermoplastic statorover mold member 170 including a central elongated and generallycylindrically shaped hollow core or tube 172 defining an interiorelongate cylindrical through-aperture or hole 140, an upper peripheralcollar 175 defining an interior receptacle or housing 175 a, an upperinterior collar 144 surrounding the tube 172 and defining an upper ringshaped interior bearing receiving shoulder or pocket or nest 178 definedin the interior of the tube 172, and a lower collar 142 defining a lowerinterior bearing receiving shoulder or pocket or nest 180.

The rotor assembly 114 includes a generally disc and cup shaped magnet132 including a disc shaped base 131 defining a central through-hole oraperture 134 and a peripheral and circumferentially extending andupstanding wall or lip or rim 135 together with the base 131 defining aninterior metal pole piece receptacle 137.

A washer shaped metal pole piece 136 is adapted to be located and seatedin the interior receptacle 137 of the magnet 132 in a relationship withthe lower exterior surface of the pole piece 136 seated and abuttedagainst the upper exterior surface of the base 131 and an exterior sidesurface abutted against the interior exterior side surface of the rim135 of the magnet 132. In the embodiment shown, the pole piece 136 is inthe form and shape of a disc or washer and defines a centralthrough-hole or aperture 138 having a diameter less than and spaced fromthe central through-hole or aperture 134 defined in the magnet 132. Themagnet 132 may be made of compression bonded Neo Ferrite magneticmaterial and is comprised of a plurality of alternating N-S poles.

The elongate and generally cylindrically shaped motor shaft 121 includesa pair of opposed distal ends 121 a and 121 b with the distal end 121 adefining a plurality of circumferentially extending exterior teeth andan interior circumferentially extending shoulder 121 c.

The various elements of the axial motor 110 are assembled and coupledtogether as described in more detail below.

Initially, the respective bobbins 126 with the respective electricalcoil packs 128 wound thereon are slid onto the respective statorarmature posts 125. The respective terminals 129 are then inserted intothe interior of the respective bobbin connectors 126 a and coupled tothe respective distal ends 128 a of the respective coils 128. Theshorting ring 131 is then seated against the top of the bobbins 126 in arelationship with the respective terminals 131 b of the shorting ring131 inserted into the interior of the respective bobbin connectors 126 band coupled to the respective distal ends 128 b of the respective coilpacks 128.

The stator member 170 is then over molded onto the stator assembly 112via an injection molding or the like process in a relationship with thecentral core or tube 172 defined by the over mold material extendingthrough the center of the stator assembly 170 and the remainingthermoplastic over mold material surrounding and enveloping the exteriorside surfaces of the respective bobbins 126, the bobbin connectors 126 aand 126 b, the coils 128, and all of the exterior surfaces of theshorting ring 131.

In accordance with the present invention, the use of an over moldedstator member 170 with a central hollow bearing sleeve bushing or tube172 with respective collars 144 and 142 defining respective upper andlower bearing receiving pockets or nests 178 and 180 advantageouslyreduces the cost of the motor 110, simplifies the motor assemblyprocess, minimizes stack up tolerances, and secures the bobbins 126,coils 128, terminals 129, and the shorting ring 131 against vibrationand increases thermal conductivity.

The rotor assembly 114 is then assembled as follows: the bearing 118 isseated in the interior of the collar 144 and the top bearing pocket 178defined in the sleeve 172 of the stator over mold member 170; the magnet132 is inserted and seated in the top recess or receptacle or housing175 a defined in the stator over mold member 170 in a relationshipsurrounding and spaced from the bearing 118; the pole piece 136 isinserted and seated in the interior of the magnet 132 in a relationshipwith the lower exterior surface of the pole piece 136 seated and abuttedagainst the top exterior surface of the bearing 118; the motor shaft 121is inserted through the motor 110 successively through the centralthrough-holes defined in the pole piece 136, the magnet 132, the bearing118, the stator over mold member 170, and the stator assembly 112 into arelationship wherein the bearing 118 is interference fitted around thedistal end 121 a of the motor shaft 121 and the opposed distal end 121 bof the motor shaft 121 is located in the central through-hole 124defined in the stator armature 122.

The lower bearing 120 is then inserted into the through-hole defined inthe stator armature 122 and into the collar 142 and the lower statorover mold member pocket or nest 180 into a relationship surrounding andinterference fitted to the distal end 121 b of the motor shaft 121.

The respective bearings 118 and 120 are similar in structure andfunction to the bearings 20, 20 a, and 20 b and thus the earlierdescription of the elements and features and function of the bearings20, 20 a, and 20 b is incorporated herein by reference with respect tothe bearings 118 and 120 and thus it is understood that the respectivebearings 118 and 120 include respective bearing stacked races 162 and164 corresponding in structure to the respective races 62 and 64 of thebearing 20.

In accordance with the present invention, the thrust and/or radialbearings 118 and 120 are mounted in the motor 110 and, morespecifically, are mounted in the respective opposed and spaced apartcollars 144 and 142 defined in the sleeve bushing defined by the centraltube 172 of the stator over mold member 170 in an opposed, spaced apart,and back to back relationship, and still more specifically in arelationship with the respective races 164 of the respective bearings118 and 120 in an opposed, spaced apart, and back to back relationship,to allow the bearings 118 and 120 to take up the axial forces, generallydesignated with the arrows F in FIG. 11, which are applied to the motor110 and the motor shaft 121.

More specifically, the thrust and/or radial bearings 118 and 120 mountthe motor shaft 121 in the axial motor 110 for radial movement androtation with the rotor assembly 114 relative to the stator assembly112; the top bearing 118 mounts the top portion or end of the motorshaft 121 to the stator assembly 112 for rotation relative to the statorassembly 112 and prevents the downward axial sliding or movement of themotor shaft 121 in the motor 110 in response to the application of adownward axial force F on the motor shaft 121 as shown in FIG. 11; andthe lower bearing 120 mounts the lower portion or end of the motor shaft121 to the stator assembly 112 for rotation relative to the statorassembly 112 and prevents the upward axial sliding or movement of themotor shaft 121 in the motor 110 in response to the application of anupward axial force F on the motor shaft 121 as shown in FIG. 11.

The bearings 118 and 120 are also adapted to take up some of the radialforces and can be of the same or different size or style depending uponthe particular motor application.

FIG. 14 depicts an alternate embodiment of a rotor 214 for the axialbrushless motors 10 and 110.

The rotor 214 is comprised of a generally cup or bowl shaped magnet 220that is made from a suitable magnetic material and includes a generallyflat and disc shaped base 222 with opposed top and bottom exteriorsurfaces 222 a and 222 b respectively and defining a central aperture orthrough-hole 228. The magnet 220 additionally includes a peripheral andcircumferentially extending wall or lip or rim 230 extending unitarilyoutwardly and upwardly from the peripheral top exterior surface 222 a ofthe base 222 of the magnet 220 to define a generally cup or bowl shapedmagnet 220 defining an interior cavity or receptacle 232. In theembodiment shown, the magnet 220 is a multi-pole magnet and morespecifically an eight pole magnet.

The rotor 214 further includes a generally washer shaped metal polepiece 234 that is seated in the magnet 220 and, more specifically, ametal pole piece 234 seated in the interior cavity or receptacle 232 ofthe cupped magnet 220 in a relationship with the bottom exterior surfaceof the pole piece 234 seated and abutted against the top exteriorsurface 222 a of the base 222 of the magnet 220 and the side exteriorsurface of the pole piece 234 abutted against the interior face of thecircumferential wall or lip 230 of the magnet 220.

In the embodiment show, a circumferentially extending magnet flux notchor angled exterior surface 236 is formed and defined in a top peripheraledge of the magnet pole piece 234.

Although not described or shown in this patent application in anydetail, it is understood that the motors 10 and 110 in accordance withthe present invention are adapted for use in an actuator or the like(not shown) including a flat integrated circuit board 216 as shown inFIG. 14 mounted in a horizontal relationship overlying and spaced fromand parallel to the top exterior surface of the motor rotor 214. Theprinted circuit board 216 includes a magnetic flux field sensor mountedthereon which, in the embodiment shown, is in the form of Hall Effectswitches/latches 218 and 219 mounted to the top exterior surface of theprinted circuit board 216. Other required electronic components (notshown) are also adapted to be mounted to the top and/or bottom exteriorsurfaces of the printed circuit board 216 and adapted for sensingmagnetic flux magnitude and/or direction. The motor shaft 116 extendsthrough an aperture 223 in the printed circuit board 216.

In the embodiment shown, the rotor 214, and more specifically the cuppedmagnet 220, is positioned in a relationship with the wall or lip 230 ofthe magnet 220 positioned vertically co-linearly with and spaced fromthe Hall Effect switches/latches 218 and 219 mounted on the top exteriorsurface of the printed circuit board 216 and still more specifically ina relationship with the wall or lip 230 of the magnet 220 positioned ina relationship generally normal with and spaced from the bottom exteriorsurface of the printed circuit board 216.

As shown in FIG. 14, the magnet 220 generates a magnetic flux field thatincludes a plurality of components or segments including a firstmagnetic flux field component or segment or field generally designatedby the arrows 240 that travels generally vertically upwardly through thebody of the base 222 of the magnet 220 in a relationship generallynormal to the opposed exterior surfaces 222 a and 222 b of the magnetbase 222; a second magnetic flux field component or segment or fieldgenerally designated by the arrows 242 that travels vertically upwardlyfrom the top of the base 222 of the magnet 220 into and verticallyupwardly through the body of the peripheral rim 230 of the magnet 220;and a third magnetic flux field component or segment generallydesignated by arrows 244 that travels vertically upwardly from the topof the rim 230 of the magnet 220 through the gap between the magnet 220and through the printed circuit board 26 and then through the area orregion of the Hall Effect switches/latches 218 and 219 mounted on thetop exterior surface of the printed circuit board 216.

In accordance with the present invention, the positioning of the magnetpole piece 234 in the interior of the magnet 220 in relationship withthe notch 236 in the pole piece 234 located adjacent and opposed theinterior face of the rim 230 of the magnet 220 enhances the density ofthe magnetic flux field in the area or region of the top of the rim 230and, more specifically, allows more of the magnetic flux field to travelout and away from the peripheral rim 230 of the magnet 220 and throughthe Hall Effect switches/latches 218 and 219.

Numerous variations and modifications of the axial brushless DC motordescribed above may be effected without departing from the spirit andscope of the novel features of the invention. It is thus understood thatno limitations with respect to the structure of the axial brushless DCmotor illustrated herein is intended or should be inferred. It is, ofcourse, intended to cover by the appended claims all such modificationsas fall within the scope of the claims.

We claim:
 1. An axial brushless DC motor comprising: a stator includinga plurality of coils; a rotor including a disc-shaped base and adisc-shaped magnet coupled to the disc-shaped base, each of thedisc-shaped base and the disc-shaped magnet defining a through-aperture;an elongate sleeve extending through the stator, the sleeve defining aninterior through-aperture and a distal collar; an elongate shaftextending through the interior through-aperture of the disc-shaped base,the disc-shaped magnet, and the sleeve; and a bearing in the distalcollar of the elongate sleeve for allowing the rotation of the shaftrelative to the sleeve and the stator.
 2. The axial brushless DC motorof claim 1, further comprising a stator over mold member surrounding thecoils and defining the sleeve and a housing for the rotor.
 3. The axialbrushless DC motor of claim 1, further comprising a stator shorting ringincluding respective terminals coupled to the respective coils.
 4. Theaxial brushless DC motor of claim 1, wherein the plurality of coils arearranged in respective pairs of coils connected in parallel.
 5. Theaxial brushless DC motor of claim 1, wherein the plurality of coils arearranged in respective pairs of coils connected in series.
 6. The axialbrushless DC motor of claim 1, wherein the magnet is the form of a cupand the base defines a disc-shaped pole piece seated in the interior ofthe cup.
 7. The axial brushless DC motor of claim 1 further comprising amagnetic flux sensor, the magnet of the rotor including a rim andadapted to generate a magnetic flux, the magnetic flux being adapted totravel through the rim of the magnet and the magnetic flux sensor. 8.The axial brushless DC motor of claim 1 wherein the magnet is in theform of a cup including the rim and defining a receptacle for the basedefining a metal pole piece, the metal pole piece defining a notch in aperipheral region thereof located adjacent the rim of the magnet forenhancing the density of the magnetic flux in the region of the rim ofthe magnet and the magnetic flux sensor.
 9. An axial brushless DC motorcomprising: a stator including a plurality of coils; a stator defining asleeve; a rotor including a magnet; a motor shaft extending through thesleeve of the stator and coupled for rotation to and with the rotor; anda stator shorting ring including terminals coupled to the plurality ofcoils of the stator.
 10. An axial brushless DC motor comprising: astator; a rotor including a magnet; an elongate shaft; and the magnetbeing in the form of a cup defining a receptacle for a disc-shaped polepiece, the disc-shaped pole piece being separate from the magnet, thecup including a base defining a through-hole and the disc-shaped polepiece defining a through-hole and seated against the base of the cup,the elongate shaft extending through the through-hole in the base of themagnet and the disc-shaped pole piece respectively.